Unfortunately, it is very difficult to say what is wrong without seeing your project and data.
Usually, a such problem occurs when confusing the order of latitude and longitude.
But you have the right order.
Make sure that you have the correct order of values in the original data.
If the problem persists, please send me (support@infinity-code.com) your scene for testing.
To make it clear:
I do not need your working project. I need any (dummy) project where the problem is appears.

Example:
http://infinity-code.com/atlas/online-m … ample.html

// Create new XML and store it in customData.
        OnlineMapsXML xml1 = new OnlineMapsXML("MarkerData");
        xml1.Create("uiName", data.Name);
        xml1.Create("uiLocType", data.LocType);
        xml1.Create("uiCharts", data.Charts);
        xml1.Create("uiVhf_Tel", data.Vhf_Tel);
        xml1.Create("uiGroundtoAnchor", data.GroundtoAnchor);
        xml1.Create("uiPossibilities", data.Possibilities);
        xml1.Create("uiEnvironment", data.Environment);
        xml1.Create("uiTransportation", data.Transportation);
           
        current3d.customData = xml1;

Had all the creating of 2d and 3d markers plotting at their correct geo positions on the map with version 2.5, I've just upgraded to V3 (latest stable) and changed the create of the markers to use the 2 respective managers.

With the following code
        Debug.Log("Adding marker at:" + data.Lat + " " + data.Long);
        Vector2 markerGeo = new Vector2((float)data.Long, (float)data.Lat);
        OnlineMapsMarker3D current3d = OnlineMapsMarker3DManager.CreateItem(data.Long,data.Lat, MapMarker);
        OnlineMapsMarker current2d = OnlineMapsMarkerManager.CreateItem(data.Long,data.Lat, DefaultMarker, data.Name);

I use 2d and 3d markers in the same place and display which one depending on which camera is rendering.

The problem I have is that all the created markers are at the center of the map, even though when looking at the managers, they all have the correct coordinates set.  Any ideas?
They are all also disabled in the scene view.  As if they are outside of the map.